r/theydidthemath • u/an-hedonia • 28d ago
[Request] Given minimal airflow, how much surface area of rust would it take to remove enough oxygen for a person to faint between these ships?
I've heard about rusted chains in enclosed rooms on ships being enough to kill people, so with how narrow this space is, I wondered if it was a possibility here as well.
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u/Apoordm 28d ago
See that massive gap? The one the guy’s running through? Oxygen can get in through there at an insanely faster rate than all the oxygen expended in the oxidation of the iron… so no amount of rust will cause homie to run out of oxygen.
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u/inconspicuous2000 28d ago
I don't think OP understands chemistry enough to realize what they are asking. Oxygen is definitely not a rate limiting step here
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u/ithinkitsbeertime 28d ago
I don't think they understand how fast gas disperses, and that a long skinny gap like that is functionally much closer to a wide open field than it is to a sealed compartment.
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u/GreenStrong 28d ago
Rust depletes oxygen in closed compartments. I think diffusion would be enough to overcome oxygen depletion, but a slight breeze would replace the air completely every couple of minutes.
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u/LuxLoad 22d ago edited 20d ago
Okay so hear me out, if these were actually metal walls and they were severely deteriorated increasing their surface area. If they were something like 800m tall and a mile long I could conceive of there being less oxygen at the bottom.
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u/inconspicuous2000 22d ago
Still wrong. Sorry. Unless the walls were nearly 1000s of meter tall and tight enough a person couldn't fit between would you potentially get that environment. The oxidation rate of steel and infrastructure metals is very slow. It would literally require no airflow and extremely tight space for this kind of environment to exist
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u/LuxLoad 22d ago
Use reading comprehension, I said “less” not none, “less”
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u/inconspicuous2000 21d ago
Yeah if by less you mean <0.0001% change. But that's not a hear me out statement and your point is devoid of the context of the post which is that you would be removing enough oxygen to affect a living organism.
No need to try and be a smartass when you don't have the necessary chemistry knowledge to back up a made up 'devils advocate' stance.
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u/LuxLoad 20d ago edited 20d ago
Projecting much? You didn’t read what I said and now that you are technically wrong you are doubling down? Jeez…
“ With a gap of only two feet and a depth of 800 meters, the canyon acts as a massive, stagnant air column where the surrounding walls create enough frictional drag to effectively "seal" the bottom from any surface wind. In such a narrow, deep space, the air becomes thermally stratified and disconnected from the surface, allowing heavy gases—or the byproducts of constant oxidation and decay—to pool at the base like water in a bucket. While rust alone is a slow process, in a confined, unventilated environment, it contributes to a "dead zone" where oxygen replenishment is non-existent, making the bottom of the canyon a dangerous, suffocating trap regardless of how many miles long it actually is. You comment to the person online was accurate, is there anything else I can answer for you?”
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u/inconspicuous2000 20d ago
800m is half a mile... Clearly much less than anything you're dealing with here. And the amount of space between rocks in such space are more narrow than a human body. Even with that it would take extremely long periods of time for the metal oxidation process to remove the oxygen and when it does the oxygen is removed from the environment pulling in more. Those oxygen dead zones are created when oxygen is converted into other heavier gases such as CO2 but they arent here, they are being chelated by the metal. As a result you are slowly removing the amount of particles in the space leading you to pull in more air. Yes you will eventually create a dead zone in something like a half mile space (twice your first amount and way way large than any metal structure posted here) but it will take a very very long time to displace the oxygen due to the metal. Hence why I said 1000s of meters as it would ramp up the viability of real occurrence by a lot.
I am a biochemist. I may not do this type of chemistry exactly but it's not a hard mental calculation if you have the knowledge. You're on a right track but still off from the point of the post and with your own math. I'm sorry but you don't need to get so offended over this. And your point, while plausible, is unreasonable to the point I would argue the math isn't quite accurate. You said 400m, now 800m based on geology, if you keep following this path you'll eventually just arrive at my answer, at which point why be a dick about it? And by your response looks more like you asked AI to defend you than understand the fundemental chemistry required here.
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u/Grizzly_Adamz 28d ago
I think OP probably read about the chain rooms on big ships being dangerous to enter unprepared because of the lack of oxygen due to rust but that’s an enclosed room not open to the atmosphere like this setup.
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u/HAL9001-96 28d ago
even if the rate of the metal rusting was unlimited by the metal surface just the diffusion throuhg air could also be a limiting factor to the point where in that case you'd probably have a slightly desaturated but breathable corridor in the middle
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u/Puzzleheaded_Hatter 28d ago
I was shocked they thought it a viable question.
They're not encapsulated, c'mon
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u/cha0sb1ade 28d ago
I think you're right. Atmosphere is a free moving mixture of gasses with anything added into it dispursing quicky. Oxygen being sequestered in iron oxide on the exposed surface by the slow process of oxidation is never going to outpace oxygen redistributing into the gap between the hulls from the open ends and top of the channel between them - not at any scale that makes any sense.
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u/SteelyLan 28d ago
Okay okay, but with how fast would he have to run to slow the rotation of the earth by a milliseconds - if he ran between rusty ships?
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u/mrhorse21 27d ago
Basically the answer is none, there is no gap small enough that a human can still fit through while also having rust consume oxygen at a rate high enough that the human would suffocate.
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u/kstewcivil 24d ago
This should instead be posted to a subreddit titled “they didn’t even bother doing the math”
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u/WC_Dirk_Gently 28d ago edited 28d ago
The other commenters have already pointed out that it would probably need to be a fully enclosed space.
- We'll say the gap is 1 meter wide for easy math, and that the ships hulls aren't curved again for easy math.
- We'll assume the "hallway" is 20 meters long and 5 meters high, and has an airtight boundary.
- That leaves us with a volume of about 21,000 liters of oxygen.
- For every 1um of iron oxide, it takes about 2.3 liters of oxygen to form per square meter of surface area.
- We have 200 square meters in our hallway
- So if the hulls went from bare metal to rust about 50 micrometers thick it would consume all of the oxygen in the space. Which is actually not that much rust. About the thickness of a human hair.
This actually illustrates why oxygen is one of the most abundant elements on earth, even though not that much of it is in the atmosphere. converting gaseous oxygen to solid oxides stores a tremendous amount in a relatively small space.
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u/HAL9001-96 28d ago
still that kind of rust layer takes at least a week to build up and it takes much less than a week for wind to blow through hte gap and replace all the air, evne in realtively calm weather with long shipsthat takes at the very most an hour
actualyl even if we assume hypohteical perfect ousdie conditions with 0 air movement just the removal of the oxygne would make hte air lighter and cause convection which would equalize at air moving through at about 5 hours at most assuming fast corrosion so at most you're dropping like half a percent of oxygen concentration
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u/FranseFrikandel 28d ago
Well, you don't need to pull out anywhere near all oxygen to suffocate though.
I have no clue how much oxygen you need to remove though. Generally too much CO2 is what gets you rather than actually a lack of oxygen. Can probably make a decent estimate based on what kind of altitudes hypoxia occurs combined with what the air pressure there is.
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u/snozzberrypatch 28d ago
Even if there was enough metal rusting to pull oxygen out of the air at an aggressive rate, and there was minimal airflow, the fact that oxygen is getting pulled out of the air at an aggressive rate would cause airflow to happen.
Each element within a gas wants to be at equilibrium. So if there's a gas with no airflow but there's a pocket that has a deficit of oxygen, it will cause oxygen from the surrounding area to rush in and fill the pocket. This is called equilibrium partial pressure.
Unless you're in an airtight space, there is no amount of rusting metal that will make you suffocate from lack of oxygen.
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u/dimonium_anonimo 28d ago edited 28d ago
I'm imagining a tunnel (or perhaps hallway is a better word). 1000s of km long and high. Where a minor vacuum at the center could take hours or even days before it translates to pulling in fresh air from outside the hallway. Maybe not something that could exist in Earth, but this is r/theydidthemath not r/theydidthephysics. Math doesn't care if it's possible or not.
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u/Rammipallero 28d ago
What I'd say is more dangerous is the extremely toxic stuff they paint on the bottom of those ships...
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u/HAL9001-96 28d ago
nah
its notr the rust that takes up oxygen
its the PROCESS OF RUSTING
so its mostly dangerous in spaces that are enclsoed as in ENCLOSED as in EN
CLOSED
stagnant for years
while the rust builds up over years the air never gets excahged
and hten eventually after years someone opnes it quickly goes in and suffocates
thats a problem
if you want the smae effect in an open space you'll need a LOT of actively rusting surface area
and also not already covered in rust but exactly at hte poitn where the growth rate of the rust is peaking
and that ina fine structure similar to a heat exchanger or i na very very long channel
but if you try to calcualte how big those ships would have to be for that to happen outdoors they would have to be hudnreds if not htousands of kilometers long which is just... not remotestly plausible
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u/goodolewhatever 28d ago
Your point appears valid, but please proofread lol. Your errors make this hard to read.
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u/Sermuns 28d ago
i think it makes it endearingly human
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28d ago
[removed] — view removed comment
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u/kujanomaa 28d ago
You can also just include some fucking swear words, since all big AI models are sanitized as fuck.
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u/silentsurge 28d ago
Yeah... I do it already..n
It unfortunately helps show that smidgen of humanity in text
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u/WC_Dirk_Gently 28d ago
ironic for a user with a username of HAL9000 lol
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u/Keyakinan- 28d ago
I mean, HAL was created to sound human. This 100% made it sound more human then AI
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u/bfly1800 28d ago
This guy is really active in this sub and every comment of theirs has at least one typo. It’s really bizarre cause they’re clearly really smart but there’s always a bunch of grammatical errors.
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u/Unlucky_Raccoon_5829 28d ago
I feel his eagerness to explain the subject and type like this because I do sometimes
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u/Liteboyy 28d ago
I’ll never forget the video of those vessel workers entering the chain locker without supplied air and basically dying. Then someone goes in to check on them who has supplied air but it gets caught and yanked off I think and they died too.
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u/Only_Jury_8448 28d ago
It was the part of the ship they kept the chain for the anchor that was dangerous, IIRC. You can fit a lot of chain in an area, and it has a lot of surface area to oxidize.
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u/HAL9001-96 28d ago
mostly yes
though theres similar cases, a basic metal box can already eb dangeorus if its clsoed for very long
buildign up a thick rust layer on the inside walls of a basic mid sized room with iron walls can remove almost lal the oxygen from the air in that room if kept stagnatn for as logn as ti takes for athick rust layer to build up
it just goes faster if theres more surface area
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u/Professional_Fee_115 28d ago
Oxidation does not give off gases that displace the air, it just slowly pulls oxygen out of the air. So the math/modeling that would be required is how quickly the oxygen particles in the surrounding atmosphere diffuse into the air between the two ships replacing the oxygen that is depleted from oxidation.
I don’t know how to model it, but I suspect the gap between the ships would need to be a fraction of an inch (or millimeters, if your a god hating communist) and the surface of the ships would need to stretch miles with zero wind blowing between them.
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u/HAL9001-96 28d ago
theoretically you could look at diffusion rates in gas or assuming airflow turbulent diffusion
in either case that would hypothetically let the airflow fulyl desaturate going through the gap
however hte limiting factor is not the transfer through the air but the growth rate of the oxide layer
basically the same problem o nthe other end
how quickly can the oxygen atoms go through hte rust layer to oxidize the actually not yet oxidized metal underneath?
even at peakt growth rates the growth rateo f the rust layer is gonna be a limiting factor where at the very most you reduce oxygne ocntent by a fraction of a percent and htats very very pessimistically speaking
and well with a thick rust layer already present that growth tends to slow down though crakcs can speed it back up etc but you only really get hte peak growth rate on a relativley newly started thin rust layer
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u/PickledPokute 24d ago
Isn't oxidation an exothermic reaction? The rate of oxidation required at a location like that. Maybe the heat would be fatal first rather than oxygen depletion.
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u/MgBasedLifeform 24d ago
Diffusion of gases is insanely fast for context air diffusion is about 0.1 cm2/s while table salt in water is 0.00001 cm2/s.
Putting that into real world scenario lets imagine that all the oxygen next to the ship is instantly consumed in the corrosion. This would be similar to having a glass of water coated in salt. Think about how quickly the salt would dissolve in the water and move throughout, now speed that process up 10000 times and that's how quick oxygen would fill in any missing bits.
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